The present invention relates to an optical pickup device for optically recording/reproducing information on/from an optical medium, and more particularly, to an optical pickup device including a relay optical system.
Modern optical disc drives for use as external recording apparatuses for computers are expected to have an increased storage capacity and ensure higher-speed operation.
There are some approaches for increasing the storage capacity of a disc drive. The storage capacity can be increased relatively easily by making a disc for storage multi-sided. In a conventional optical disc such as a compact disc or 3.5-inch magneto-optical disc, only one side of the optical disc serves for recording/reproduction. The storage capacity of the optical disc drive can be increased if both sides of the optical disc are designed for recording/reproduction or if two or more optical discs are simultaneously loaded so that more recording surfaces can be used for recording/reproduction.
In this case, however, very high costs are entailed if an optical pickup device is mounted for each recording surface. The costs can be effectively reduced in a manner such that the optical path is changed to select one of recording surfaces for recording/reproduction so that as many components as possible can be shared among the recording surfaces. An optical disc drive of this type is disclosed in, for example, Jpn. Pat. Appln. KOKAI Publication No. 2-206037, which is incorporated herein by reference.
Supposedly, the optical path can be changed by various manners. According to a technique described in, for example, Jpn. Pat. Appln. KOKAI Publication No. 9-223327, which is incorporated herein by reference, the optical path is changed by controlling the polarization plane of incident light by a liquid crystal cell and combining it with a polarization beam splitter that is located behind the cell.
For the other requirement for higher-speed operation, a manner that uses a galvano-mirror to improve the access speed is disclosed in, for example, Jpn. Pat. Appln. KOKAI Publication No. 5-73944, which is incorporated herein by reference. According to this arrangement, focus control is effected by driving a relay lens along its optical axis, which is included in a relay optical system located in the optical path. Further, tracking control and access control are carried out by the galvano-mirror which deflects the laser beam.
A combination of the aforesaid techniques is a very effective measure to realize a high-speed, large-capacity optical disc drive.
According to an optical pickup device, the smaller the diameter of a spot formed on a disc, the higher the necessary accuracy for the adjustment of its optical components is. In the case of an optical pickup device that has a relay optical system, in particular, position adjustment for lenses and other components requires high accuracy. This is a factor that complicates adjustment for the assembly of the optical pickup device and increases the assembly cost.
In the case where the optical path is changed in the optical pickup device that includes the relay optical system, moreover, it is to be desired that an element for switching the optical path should be located in the relay optical system, in consideration of reduction in the number of essential components and the degree of freedom of layout design.
However, this arrangement requires adjustment of very high accuracy between a plurality of recording surfaces. All other lenses than one that is used in common for the optical path change must be adjusted with high accuracy for the individual recording surfaces. This also is a factor that complicates the adjustment for the assembly of the optical pickup device and increases the assembly cost.
The present invention has been contrived in consideration of these circumstances, and its object is to provide an optical pickup device having a relay optical system, which is designed so that the necessary accuracy for the position adjustment of its components is reduced, thus ensuring lower assembly cost.
Additional objects and advantages of the invention will be set forth in the description which follows, and in part will be obvious from the description, or may be learned by practice of the invention. The objects and advantages of the invention may be realized and obtained by the instrumentalities and combinations particularly pointed out hereinafter.